A Legal Aid defense lawyer dropped his briefs in a Brooklyn bar and made a motion to relieve himself – sparking a brawl that landed him and a colleague in legal trouble of their own, The Post has learned.

Court papers say Brendan Relyea, 30, grew impatient with the long line to use the men’s room at the Boat Bar on Smith Street on July 10, so he urinated on the floor, splashing a passer-by.

“I’m gonna kick your ass,” Pate told Knouff, according to the court papers, before Relyea spat in Knouff’s face and both men punched him and flung him against a roll-down gate.

When Pate and Relyea were charged with assault, menacing and harassment and Relyea with public urination, the Legal Aid Society didn’t exactly charge to their defense.

“Pending resolution of the misdemeanor charges against two Legal Aid criminal defense attorneys, they have been assigned to office duty and are not handling cases in court,” Legal Aid spokeswoman Pat Bath said.

Knouff, 28, was suspended for stoning a DUMBO bar’s window during the Brooklyn DA’s 2006 Christmas party and was fired for allegedly trying to bribe cops after getting into a tiff with a cabby in July.